Evaluation of catalytic activity of Ag and Au dendrimer-encapsulated nanoparticles in the reduction of 4-nitrophenol

LangmuirHinshelwood parameters were determined with the use of gold and silver dendrimer-encapsulated nanoparticles (Au-DENs and Ag-DENs) as catalysts. Dendrimers were used as templatingand stabilizing agents to ensure that there is no aggregation of metal nanoparticles. The synthesis ofDENs using amine terminated generation 4 poly (amido)amine dendrimer (G4-PAMAM-NH₂) was suc-cessfully demonstrated. These synthesized DENs were characterized using UVvisible spectrophotometry (UVvis), electron dispersion X-ray analysis (EDX), and Fourier transformed infrared spectrophotometry (FTIR). High resolution transmission electron microscopy (HRTEM) was used to determine the averageparticle sizes, and the average particle sizes were found to be 1.23 ± 0.13 and 1.17 ± 0.13 nm for Au- and Ag-DENs, respectively. Comparison of catalytic activity between the two metal nanoparticles was done interms of thermodynamic parameters obtained from LangmuirHinshelwood fits at 298 K. 4-Nitrophenol(NP) reduction by sodium borohydride (NaBH₄) in the presence of the synthesized DENs as homogeneouscatalysts was used by virtue of being a model reaction. Effect of diffusion barrier in all kinetic runs wasaddressed by calculations of the second Damkhler number and by the application of the second Fickslaw of diffusion. The LangmuirHinshelwood model proved to be an efficient model for thermodynamiccomparison of the two metal nanoparticles.